Cam lobe profile to accommodate mechanical lash of a switchable hydraulic lash adjuster

ABSTRACT

In an engine valve train equipped with a DHLA, the radius of the base circle of a cam lobe is decreased, relative to the radius of the base circle of a cam lobe in an engine equipped with an HLA, in proportion to the internal lash in the DHLA. The actual decrease in the base-circle radius is calculated by trigonometric relationships among the base circle portion, the length of the rocker pivot arm, and the internal lash of the DHLA. The decrease in the base circle radius is compensated by extension of the valve train lash-adjustment mechanism of the DHLA. After the internal DHLA lash is taken up during valve actuation, the coordinate position of the pivot point of the DHLA rocker arm is then identical with the coordinate position of the pivot point of an HLA rocker arm of a DHLA-equipped engine.

TECHNICAL FIELD

The present invention relates to internal combustion engines having overhead camshafts, hydraulic lash adjusters (HLAs), and rocker arms end-pivoting on the HLAs and following the cams to activate engine combustion valves; more particularly, to such engines having HLAs both with and without means for selectively engaging and disengaging such valve activation; and most particularly, to means for compensating for mechanical lash in a deactivating hydraulic lash adjuster (DHLA) to permit equal valve lift performance in engines having both HLAs and DHLAs.

BACKGROUND OF THE INVENTION

It is well known that overall fuel efficiency in a multiple-cylinder internal combustion engine can be increased by selective deactivation of the engine valves, on one or more cylinders, under certain engine load conditions. For cam-in-head engines, a known approach to providing selective deactivation is to equip the HLAs for those valves with means whereby the rocker arms may be rendered incapable of transferring the cyclic motion of engine overhead cams into reciprocal motion of the associated valves. See, for example, U.S. Pat. No. 6,321,704 B1. Typically, a DHLA includes, in addition to the conventional means for hydraulic lash elimination in the valve train, concentric inner and outer portions which are mechanically responsive to the cam lobe and which may be selectively latched and unlatched hydromechanically to each other, typically by the selective engagement of pressurized engine oil to drive spring-loaded latch pins in the inner portion.

In manufacturing generally, it is beneficial to maximize the use of standard components. Thus, in the automotive industry it is standard practice to use identical roller finger followers and camshafts having identical lobe base circle diameters on engines having HLAs and DHLAs. However, DHLAs typically are provided with an amount of intended axial mechanical lash in the components to increase the reliability of the locking mechanism extending from the pin housing to engage the locking feature, such as a groove, in the HLA body. The DHLA's hydraulic lash adjustment mechanism cannot compensate for this built-in mechanical lash. Consequently, since the mechanical lash must be taken up first by the DHLA valve train before the associated valve begins to open, the actual valve lift of a prior art valve train employing locked DHLAs and using a cam lobe designed for a conventional HLA is reduced compared to that of an identical valve train employing HLAs. It is reduced because part of the cam eccentric designed to lift the valve is instead used to compress the length of the DHLA by an amount equal to the mechanical lash. Further, because the pivot center is lowered relative to the HLA counterpart, the timing of the valve opening, maximum lift, and closing are affected as well. Also, the change in effective operating geometry causes changes to the resulting force vectors associated with the DHLA valve trains and leads to further differences in the operating kinematics between the DHLA valve trains and the HLA valve trains. These differences are counter to the objective to reducing variation between the valve trains.

The current remedy of simply adding lash ramps to both the opening slope and the closing slope of the associated cam lobe (along with an increase in maximum lobe height) to accommodate the additional travel of the pin housing within the body due to the mechanical lash, does nothing to keep the pivot centers from shifting. Thus, while differences in valve lift profiles can be eliminated, the variation of force vectors and operating kinematics caused by the shifting pivot centers remain. In addition, with the current remedy, the cam polar coordinates of the HLA cam lobes and the DHLA cam lobes must be made different in order to produce identical valve motion, and, in order to achieve identical valve lift timing, the reference angle locating the maximum lift point on the DHLA cam lobe must be angularly shifted relative to the reference angle locating the maximum lift point on the HLA cam lobe. These adjustments needlessly complicate the camshaft grind specifications and increase the chance of errors when fabricating the camshaft.

What is needed in the art is a simple compensation that can be provided inexpensively in engine manufacture such that the valve lift, valve timing, and effective operating geometry of systems with both HLAs and DHLA components are identical.

It is a principal object of the present invention to provide equal valve lift performance in like engines having HLAs and DHLAs that does not cause the pivot center points of the DHLA rocker arms to shift away from the pivot center points of the HLA rocker arms.

SUMMARY OF THE INVENTION

Briefly described, in an engine valve train equipped with a DHLA, in accordance with the present invention the radius of the base circle portion of an associated cam lobe is decreased, relative to the radius of the base circle portion of a cam lobe on the same camshaft associated with an HLA, by an amount proportional to the internal mechanical lash in the DHLA. The surface coordinates of the cam eccentric are unchanged except for the addition of entry and exit ramps which provide the necessary transition to the reduced-diameter base circle portion. The actual decrease in the base-circle radius is calculated by simple trigonometric relationships among the base circle portion, the length of the rocker arm pivot axis, and the internal lash of the DHLA. The decrease in the base circle radius is exactly compensated by extension of the valve train lash-adjustment mechanism of the DHLA with respect to the locked position of the device. The net effect of this improvement is that after the internal DHLA lash is taken up by the rotating cam lobe, the coordinate position of the pivot point of the rocker arm on the associated DHLA is identical to the coordinate position of the pivot point associated with an HLA on the same camshaft at a point when the valve lift event begins to occur. The resulting valve train geometry and operating kinematics is therefore identical for the deactivating and non deactivation valve trains.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is an elevational cross-sectional view of a prior art non-deactivating HLA;

FIG. 2 is an elevational cross-sectional view of a prior art deactivating DHLA, lo substantially as disclosed in U.S. Pat. No. 6,321,704 B1;

FIG. 3 are schematic drawings of a prior art HLA valve train including the HLA shown in FIG. 1;

FIGS. 4 a and 4 b are schematic drawings of a prior art DHLA valve train including the DHLA shown in FIG. 2, showing the effect of mechanical lash within the DHLA; and

FIGS. 5 a and 5 b are schematic drawings of a HLA valve train (5 a) and of a DHLA valve train (5 b), in accordance with the present invention, showing correct compensation for mechanical lash within the DHLA.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a prior art HLA 10 having a longitudinal axis 11 is shown. A cylindrical, hollow HLA body 12 receives a slidable piston 14 urged outwards by a bias spring 16 disposed in a high-pressure chamber 18. Piston 14 includes a low-pressure reservoir 20 that receives pressurized oil from an engine oil gallery (not shown) via connecting ports 22,24. A check valve 26 passes oil from reservoir 20 to chamber 18 as needed to support piston 14 in any lash-adjusting extension within body 12 as required by a valve train in which HLA 10 is installed. Piston 14 includes a hemispherical head 28 for pivotably receiving a hemispherical socket 29 of a rocker arm 31, such as for example, a roller finger follower, as described below. Rocker arm 31 includes a roller 33, mounted on axis 34, for following the base circle portion 35, having a constant radius, and eccentric portion 37 (entrance ramp 39, nose 41, and exit ramp 43) of a camshaft lobe 45. An opposite end of rocker arm 31 includes an arcuate pad 47 for engaging a stem 49 of a combustion valve in an internal combustion engine. Arcuate pad 47 is defined by a radius 51 and a center 53 which, together with the pivot center 55 of socket 29 and head 28, define a pivot arm 57 for rocker arm 31.

Referring specifically to FIG. 3, prior art HLA 10 in conjunction with its associated RFF, combustion valve and cam lobe (HLA valve train), as the HLA valve train relates to internal combustion engine 152, is shown. The left view shows the HLA valve train on base circle of the cam lobe (closed valve) where roller 33 just reaches the beginning of entrance ramp 39 of camshaft lobe 45; the right view shows the HLA valve train at maximum valve lift. In both views, distance A is the vertical distance between the pivot center 55 and the axis of rotation 58 of the cam lobe. In both views, dimension A is the same. Circle 59, shown in the right view, represents an arbitrary fixed reference point on the cam shaft from which the angular position of the maximum cam radius of each cam lobe is positioned. The angle R represents the angle from the reference point to the maximum cam radius of the particular cam lobe shown.

Referring to FIG. 2, prior art DHLA 110 having a longitudinal axis 111 is substantially as disclosed in U.S. Pat. No. 6,321,704 B1, the relevant disclosure of which is incorporated herein by reference. DHLA 110 has a generally cylindrical adjuster body 112. A pin housing 114 is slidably disposed within a first axial bore 115 in adjuster body 112. Pin housing 114 itself has a second axial bore 130 for slidably receiving a piston 132 having a hemispherical head 128 for receiving a socket end (not shown) of a roller finger follower in an overhead-cam engine valve train. Pin housing 114 has a transverse bore 134 slidably receivable of two opposed locking pins 136 separated by a pin-locking spring 138 disposed in compression therebetween. First axial bore 115 in adjuster body 112 is provided with a circumferential groove 140 for receiving the outer ends of locking pins 136, thrust outwards by spring 138 when pins 136 are axially aligned with groove 140. In such configuration, DHLA 110 is in valve-activation mode. (As shown in FIG. 2, DHLA 110 is in valve-deactivation mode.) Upper end 142 of pin housing 114 defines a first seat for a loss-of-motion (LM) return spring 144 disposed within an annular chamber 146 formed between bore 115 and pin housing 114. LM spring 144 finds a second seat at an annular stop 148 in bore 115. Groove 140 further defines a reservoir for providing high pressure oil against the outer ends of locking pins 136 to overcome spring 138 and retract the locking pins into bore 134, thereby unlocking the pin housing from the adjuster body to deactivate the adjuster. Groove 140 is in communication via at least one port 150 with an oil gallery (not shown) in engine 152, which in turn is supplied with high pressure oil by an engine control module (not shown) under predetermined engine parameters in which deactivation of valves is desired. Piston 132 includes a hydraulic element assembly (HEA) 126 lodged at an inner end thereof. HEA 126 comprises a spring loaded check ball 154 lodged against a seat 156 formed in piston 132 separating a low-pressure oil reservoir 120 from a high-pressure chamber 118 formed between HEA 126 and pin housing 114.

The purpose of describing in detail thus far the arrangement of prior art DHLA 110 is to permit description of the source of mechanical lash within DHLA 110, which is the source of the problem solved by the present invention.

The outward travel of pin housing 114 within bore 115 is limited by engagement of housing stop 158 with stop 148. The axial thickness of housing stop 158 is selected such that the lower edges 160 of pins 136 can readily clear the lower edge of groove 140 during locking of DHLA 110. A desired clearance of typically about 0.250 mm is provided, defining an internal axial mechanical lash within DHLA 110.

Referring to FIGS. 4 a and 4 b, a prior art DHLA 110 in conjunction with its associated RFF, combustion valve and cam lobe (DHLA valve train) is shown. FIG. 4 a shows the DHLA valve train before the internal axial mechanical lash within DHLA 110 is taken up; FIG. 4 b shows the DHLA valve train just after the internal axial lash within DHLA is taken up (and immediately before valve 49 begins to open), wherein cam lobe 45 has rotated slightly from its position shown in FIG. 4 a. For clarity of comparison, FIG. 4 b is shown as a mirror image of FIG. 4 a.

Referring now to FIG. 4 a, when the locking pins are engaged in valve-activation mode of DHLA 110, as roller 33 reaches the beginning of entrance ramp 39 of the cam lobe, the internal axial mechanical lash has not yet been taken up. At that point, dimension A, being the vertical dimension between pivot center 55 and the axis of rotation 58 of the cam lobe, is shown. In the prior art, dimension A at the point of rotation of cam lobe 45, as shown in FIG. 4 a, is identical to a dimension A in an HLA (non-deactivating) valve train. Therefore, the coordinate position of the pivot point of the rocker arm on the associated DHLA is identical to the coordinate position of the pivot point associated with an HLA on the same camshaft, assuming that both FIGS. 4 a and 4 b are on the same coordinate systems, that is, the origin of the coordinates being the axis of rotation 58 of the cam lobe and the y axes of the coordinate systems being the same.

Referring now to FIGS. 2 and 4 b, the camshaft has continued its rotation and roller 33 has started up entrance ramp 39. Pin housing 114 and piston 132 will travel against the force of LM return spring 144, along axis 111 into body 112 until extended pins 136 engage the lower edge of groove 140, after which head 128 becomes a firm pivot for the rocker arm socket. Pivot center 55′ is displaced from a first position A to a second and lower position A+X by the rotational force of the camshaft acting against the LM spring 144, all before any valve-opening motion is induced in pad 47. Thus, it will be seen that part of the intended valve-lifting effect of a cam eccentric is lost to the taking up of this mechanical lash at the start of each valve-opening cycle. Therefore, the coordinate position of the pivot point of the rocker arm on the associated DHLA (55′ in FIG. 4 b) is not identical to the coordinate position of the pivot point associated with an HLA (55 in FIG. 4 a) on the same camshaft (assuming again that their coordinate systems are the same).

The shift in the coordinate position of pivot center 55′ to A+X fundamentally changes the relationship between the pivoting follower and the cam lobe and therefore must be accounted for in order to achieve identical valve lift and valve lift timing between the HLA and DHLA valve trains. It is possible to eliminate any lift and/or timing variation by using the actual A+X pivot point in the calculations of the cam lobe contour and by shifting angle β (that is, using an angle β for the DHLA valve trains that differs from angle β for the HLA valve trains). In this case, the valve lifting portion of the lobe contour and angle β of the cam lobes associated with the DHLA valve trains would be unique thereby complicating the grind parameters of the cam shaft lobes.

Thus, while it is possible to exactly match the valve lift of the DHLA valve train with the valve lift of the HLA valve train, there is no way to achieve identical geometry and operating kinematics between the DHLA and HLA valve trains because of the shifting pivot point 55. In other words, the shift in the pivot center from A to A+X causes changes to the resulting force vectors and operating kinematics acting on the DHLA valve train which introduces undesired variation between the DHLA and HLA valve trains.

By comparing FIG. 5 a to FIG. 5 b, the solution to the lash problem provided by the present invention is shown. (For clarity of comparison, FIG. 5 b is shown in mirror image position of FIG. 5 a). FIG. 5 a shows the HLA (non-deactivating) valve train as shown in FIG. 3. Roller 33 is in contact with base circle 35 of the associated cam lobe. Distance A is the vertical distance between the pivot center 55 and the axis of rotation 58 of the cam lobe.

FIG. 5 b shows the DHVA valve train in accordance with the invention. Roller 33 is in contact with base circle 35′ and before the roller reaches the beginning of entrance ramp 39′ of cam lobe 45′ (the internal axial mechanical lash has not yet been taken up). The invention provides for the coordinate position of the pivot point of the rocker arm on the associated DHLA relative to the axis of its cam lobe, after lash removal, to be identical to the coordinate position of the pivot point associated with an HLA relative to the axis of its cam lobe. This is done by raising the position of the lash-included pivot point of the DHLA rocker arm to a new pivot point 55″ FIG. 5 b, so that the coordinate position of the pivot point of the rocker arm on the associated DHLA, after the mechanical lash is taken up by the rotating cam lobe, is identical to the coordinate position of the pivot point associated with the rocker arm of the HLA on the same camshaft (again assuming that the coordinate systems being used as reference are the same as defined above). This is readily accomplished by reducing proportionally the radius R′ of base circle 35′ as compared to R of base circle 35 in FIG. 5 a, allowing rocker arm roller 33 to assume a new position A−X closer to the axis of rotation 58 of base circle 35′ of the cam lobe (through extension of the HLA lash adjusting mechanism 126 (FIG. 2)). It will be seen that the amount of radius reduction, proportional to lash allowance mechanical lash and to be applied during manufacture of the camshaft, may be calculated readily by simple trigonometric relationships, depending upon the radii of roller 33 and base circle 35′, the distance of roller axis 34 from pivot points 53 and 55 (see FIGS. 3), and the known axial mechanical lash within DHLA 110.

Since, presently, the particular grind criteria must be calculated and set for each cam lobe of a given cam shaft, a decrease of the base circle radius (along with the addition of suitable entrance and exit ramps) of each lobe dedicated to a DHLA, coupled to the identical polar coordinates for the high lift portion of the cam lobe may be achieved with no or little cost added to the cost of manufacturing the cam shaft. On the other hand, the improvement allows identical valve lift, valve lift timing, and identical operating geometries and operating kinematics to be achieved regardless of whether the valve is in a DHLA position or in a conventional HLA position.

While the invention described herein is shown in a DHLA valve train having the HLA pivot point at one end of the rocker arm, the valve stem contact pad at the other end of the rocker arm and the rocker arm roller between the pivot point and pad, it is understood that components of the rocker arm may be in any order or relationship, including the rocker arm roller on one end, the valve stem contact pad on the other end of the rocker arm and the HLA pivot point between the roller and pad.

While the invention has been described by reference to various specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but will have full scope defined by the language of the following claims. 

1. In a valve train system for an internal combustion engine wherein the valve train system includes an HLA valve train and a DHLA valve train, said valve train system comprising: a DHLA in the DHLA valve train pivotably supportive of an associated rocker arm for selectively actuating an associated engine combustion valve in response to a movement of a first actuating member engaged by a contact surface of said associated rocker arm, wherein said rocker arm associated with the DHLA includes a pivot point for pivoting on the DHLA, and wherein said first actuating member includes a base contour portion, lift portion and an axis of rotation, an HLA in the HLA valve train pivotably supportive of an associated rocker arm for selectively actuating an associated engine combustion valve in response to a movement of a second actuating member engaged by a contact surface of said associated rocker arm, wherein said rocker arm associated with the HLA includes a pivot point for pivoting on the HLA, and wherein said second actuating member includes a base contour portion, lift portion and an axis of rotation equal to the axis of rotation of said first actuating member, the DHLA having a first length of internal axial mechanical lash that is taken up by axial compression of the DHLA during passage of the lift portion of the first actuating member past the contact surface of the associated rocker arm, the base contour portion of the first actuating member selected to included a radius for positioning the pivot point of the rocker arm associated with the DHLA at a first coordinate position in space relative to the axis of rotation of said first actuating member, such that said pivot point is displaced by said axial compression from said first coordinate position in space to a second coordinate position in space relative to the axis of rotation of said first actuating member, for pivoting of said associated rocker arm to actuate said valve, the pivot point of said rocker arm associated with the HLA being positioned at a third coordinate position in space relative to the axis of rotation of said second actuating member, wherein, on a same coordinate system having its origin at said axis of rotation of said first actuating member and a y axis, the second coordinate position in space is substantially identical to the third coordinate position in space.
 2. The valve train system in accordance with claim 1 wherein the base contour portion of the second actuating member further includes a radius for positioning the pivot point of the rocker arm associated with the HLA at said third coordinate position in space and wherein the base contour of the second actuating member is larger than the radius of the base contour of said first actuating member.
 3. The valve train system in accordance with claim 1 wherein said rocker arm is a finger follower.
 4. The valve train system in accordance with claim 3 wherein said finger follower is a roller finger follower.
 5. The apparatus in accordance with claim 1 wherein said rocker arm contact surface is disposed intermediate of said rocker arm.
 6. An internal combustion engine comprising a valve train system including an HLA valve train and a DHLA valve train, wherein said Valve train system includes a DHLA, a first rocker arm pivotably supported by said DHLA, an engine combustion valve actuated by said first rocker arm, and a first cam lobe engaged by a contact surface in said first rocker arm, wherein said first cam lobe includes a base circle portion, an eccentric portion and an axis of rotation, an HLA pivotably supportive of a second rocker arm, an engine combustion valve actuated by said second rocker arm, and a second cam lobe engaged by a contact surface in said second rocker arm, wherein said second cam lobe includes a base circle portion, an eccentric portion and an axis of rotation, wherein said DHLA has a first length of internal axial mechanical lash that is taken up by axial compression of said DHLA during passage of said eccentric portion past the contact surface of the first rocker arm, wherein the base circle portion of the first cam lobe further includes a first radius for positioning the contact surface of said first rocker arm at a first coordinate position in space relative to the axis of rotation of said first cam lobe, such that said pivot point of said first rocker arm is displaced by said axial compression from said first coordinate position to a second coordinate position in space relative to the axis of rotation of said first cam lobe, for pivoting of said first rocker arm to actuate said valve, wherein the pivot point of said second rocker arm associated with the HLA is positioned at a third coordinate position in space relative to the axis of rotation of the first cam lobe to actuate said valve, and wherein, on a same coordinate system having its origin at said axis of rotation of said first cam lobe and a y axis, the second coordinate position in space is substantially identical to the third coordinate position in space.
 7. The engine in accordance with claim 6 wherein the base circle portion of the second cam lobe further includes a radius for positioning the pivot point of the second rocker arm associated with the HLA at said third coordinate position in space and wherein the base circle of the second cam lobe is larger than the radius of the base circle of said first cam lobe. 